With James Cameron's epic currently playing in 3D, this "Titanic" comes across as a ponderous, decidedly two-dimensional retelling.

Writer Julian Fellowes’ colossal success with “Downton Abbey” offers the main selling point to check out “Titanic,” an international co-production getting a low-key kiss-off (more on that later) from ABC. Nobody has exclusive claim to the saga of the doomed boat, but to properly revisit a story that became a movie everyone and their mother saw — like, twice — one needs to bring better luggage than this. Handsome but convoluted, the four-part production certainly explores class distinctions, but juggles too many characters, too awkwardly, to yield much impact. With James Cameron’s epic currently playing in 3D, this “Titanic” comes across as a ponderous, decidedly two-dimensional retelling.

ABC clearly appears to recognize it has a ship that’s not entirely seaworthy on its hands, burning off the first three hours Saturday, with the finale airing the following night, coinciding with the 100-year anniversary of the ship’s sinking. In TV terms, that’s the sort of real estate normally reserved for reruns and mixed-martial arts.

Working with director Jon Jones, Fellowes conveys much of the same upper-deck/lower-deck politics in “Titanic” that made “Downton” such a heady experience, and of course the two occupy the same early-20th-century window.

Any similarity, however, pretty much ends there, as the first hour races through introducing a wide range of characters — lords and ladies, as well as servants, maids and stewards — before the ship’s fatal collision with an iceberg. What ensues, in each subsequent chapter, are drips of backstory and detail about various subplots, with scenes witnessed fleetingly in the premiere returning with more context, and viewed from different angles.

In theory, it’s an interesting approach, but all Fellowes really does is underscore how shrewd Cameron was in focusing on a single doomed romance against this sweeping backdrop. By contrast, while this could be turned into a lengthy anthology — think “Tales of the Titanic” — at four hours (or really three minus commercials), it’s either too much, or too little.

“Titanic” founders despite a gaudy array of talent, including Linus Roache as a British Earl, Toby Jones as an officious little man well aware he’s in second class, Lyndsey Marshal as a ladies’ maid, and so on. The problem is the chapters juggle so many characters there’s not enough time to become particularly invested in any of them, even after the ship begins to go down.

That’s not to say the project (producer Nigel Stafford-Clark gets “created by” credit, incidentally, even though Fellowes wrote it) is without moving scenes; indeed, the reason Titanic endures is because the story has proven tailor-made to acts of selflessness and bravery, as well as cowardice. There is also considerable cruelty in the young sparks of romance — including one involving the Earl’s daughter Georgiana (Perdita Weeks) — given the horror that awaits.

The Titanic centennial was inevitably going to produce a flurry of remembrances, and it’s hard to blame anyone for seeking to ride in its wake. That said, ABC’s Saturday-heavy scheduling suggests buyer’s remorse, at least on this side of the Atlantic.

So while “Titanic” wants to capture the macro and the micro, the miniseries has to be viewed through the lens of earlier voyages. And by that measure, this stately effort manages to be too big, and not nearly big enough.